By means of genetic and biochemical procedures, it is proposed to analyze the mechanisms that control the biosynthesis of the two amino acids, isoleucine and valine, in Escherichia coli. Highest priority will be given to determining the nucleotide sequence of those regions of DNA in the ilv gene cluster that are the sites for transcription initiation and transcription termination, the two processes thought to be the primary means of controlling the levels of the isoleucine and valine biosynthetic enzymes. The source of DNA will be cloned fragments derived from phages carrying defined lengths of the ilv gene cluster. Also important will be the determination of the portions of the ilv gene cluster that are actually transcribed. Another project will be to study the interaction between the ilvC promoter and upsilon, the protein required for induction of the ilvC gene. The "constitutive" upsilon which requires no inducer will be examined primarily. ilv-lac fusions will be studied both in vivo and in vitro in an effort to account for the non-coordinate expression of the ilv operon. The valine-insensitive acetohydroxybutyrate synthase will be purified.